A variable magnification optical system comprising, in order from an object side, a first lens group having negative refractive power, a first intermediate lens group having positive refractive power, a second intermediate lens group having negative refractive power and a rear lens group; upon varying a magnification from a wide angle end state to a telephoto end state, a distance between the first lens group and the first intermediate lens group being varied, a distance between the first intermediate lens group and the second intermediate lens group being varied, and a distance between the second intermediate lens group and the rear lens group being varied; the rear lens group comprising at least one focusing lens group which is moved upon carrying out focusing from an infinitely distant object to a closely distant object; and predetermined conditional expressions being satisfied, thereby the focusing lens group(s) being reduced in weight.

A composite optical element includes a glass lens and a resin lens that are joined together. The resin lens has an aspheric shape. When Nd is a refractive index of the resin lens, ?d is an Abbe number of the resin lens, and ?gF is a partial dispersion ratio of the resin lens, Nd, ?d, and ?gF are appropriately set.

A zoom lens includes, in order from an object side to an image side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and three or more lens units. A distance between adjacent lens units varies during zooming. A predetermined condition is satisfied.

A lens assembly includes a first lens group, a second lens group, a third lens group, a fourth lens group, a fifth lens group, a sixth lens group, and a first reflective element. The first and third lens groups are with negative refractive power. The second and fourth lens groups are with positive refractive power. The fifth and sixth lens groups are with refractive power. The first, second, third, fourth, fifth, and sixth lens groups are arranged in order from a first side to a second side along an axis. The first reflective element includes a first reflective surface. A light from the first side sequentially passes through the first, second, third, fourth, fifth, and sixth lens groups to the second side. The first reflective element is disposed between the first lens group and the sixth lens group.

A projection lens includes a plurality of lens groups each formed of at least one lens, and a lens barrel adapted to support each of the lens groups from an outer circumferential side. The lens barrel includes a first temporarily holding mechanism allowing the first lens group located at an end on a enlargement side to be displaced in a direction perpendicular to the optical axis, a first adhesive applied to the first temporarily holding mechanism to fix the first lens group so as to be unable to be displaced, a second temporarily holding mechanism allowing the seventh lens group located at an end on a reduction side to be displaced in a direction perpendicular to the optical axis, and a second adhesive applied to the second temporarily holding mechanism to fix the seventh lens group so as to be unable to be displaced.

A plurality of lens units of a zoom lens according to an aspect of the embodiments includes a first lens unit having a negative refractive power, and a rear lens group which includes one or more lens units and has a positive refractive power as a whole. The first lens unit consists of a first negative lens, a second negative lens, and a positive lens which are disposed in order from an object side to an image side. A specific gravity of the first negative lens, a focal length of the second negative lens, and a focal length of the first lens unit are appropriately determined.

A projection lens includes a plurality of lens groups each formed of at least one lens, and a lens barrel adapted to support each of the lens groups from an outer circumferential side. The lens barrel includes a first temporarily holding mechanism allowing the first lens group located at an end on a enlargement side to be displaced in a direction perpendicular to the optical axis, a first adhesive applied to the first temporarily holding mechanism to fix the first lens group so as to be unable to be displaced, a second temporarily holding mechanism allowing the seventh lens group located at an end on a reduction side to be displaced in a direction perpendicular to the optical axis, and a second adhesive applied to the second temporarily holding mechanism to fix the seventh lens group so as to be unable to be displaced.

Binoculars and an ocular lens have an excellent optical performance. Binoculars include: a first lens-barrel and a second lens-barrel having an objective lens and an ocular lens; and an Abbe-Koenig prism which is an erecting optical element included in the first lens-barrel and the second lens-barrel, and is characterized in that the product of an effective diameter (mm) of the objective lens and the real field of view () is 450 mm or larger.

The present invention relates to the field of optical lenses and provides a zoom lens consisting of, from an object side to an image side in sequence, a first lens having negative refractive power, a second lens group having positive refractive power, a fifth lens having positive refractive power, and a sixth lens having negative refractive power. During zooming, a distance between adjacent lenses or between lens and adjacent lens group in a direction of an optic axis varies. The second lens group consists of a second lens having positive refractive power, a third lens having negative refractive power, and a fourth lens having negative refractive power, and following conditions are satisfied: f_Tele/f_Wide?1.80; ?1.75?f3/f2??1.35; ?1.75?f4/f2??1.35. The present invention becomes compact when contracted, while during imaging, FNO is bright, and has good optical properties.

A projection system includes a first lens group that does not move when the projection magnification is changed with the aid of the zoom function, and the first lens group includes a correction lens group that is moved in the direction of the optical axis to correct worsened astigmatism. The projection system satisfies the following conditional expressions (1) and (2):

|BF20|<PFNO2(1)

1.5<|f1/f|(2)

where P represents the pixel pitch in an image displayed by liquid crystal panels, FNO represents the F number of the entire lens system, BF represents the amount of movement of the back focus position in a case where the correction lens group is moved by the amount of movement for correction of the aberration that changes when the temperature changes by 20 C., f represents the focal length of the entire lens system, and f1 represents the focal length of the correction lens group.